Starting at midnight, North County's Sprinter light-rail will shut down for up to four months due to brake "maintenance issues," the North County Transit District said Friday afternoon.

The agency said the length of closure is unknown "but may last from 60 to 120 days."

During the closure, buses will be used to ferry the thousands of passengers who use the Sprinter along its Oceanside to Escondido corridor, the agency said. It said it had been developing such a plan "for the past week."

"The primary concern of the transit agency is the safety and welfare of our passengers and staff. NCTD is taking every prudent measure to assure the safety of our riders and at the same time to continue to serve the transit public," Friday afternoon's NCTD statement said.

This weekend, NCTD will operate special express buses between the Oceanside Transit Center and the Escondido Transit Center. The express buses will run every 30 minutes and make stops at Vista Transit Center, Palomar College and Cal State San Marcos.

Bus replacement plans beyond this weekend are still in the works, the agency said. It encouraged the public to check its website at www.gonctd.com.

Earlier Friday, the agency canceled a Saturday event to celebrate the fifth anniversary of the light-rail system. Officials confirmed on Friday night they were investigating rapid wear on the trains’ central braking system.

Sprinter trains continued to run Friday morning, but at reduced speeds due to concerns over the braking system, said Frances Schnall, an NCTD spokeswoman. The slowdown was expected to delay Friday's remaining Sprinter trips by up to 30 minutes, the agency reported.

The decision to slow the speed of the trains was voluntary, and was made out of an abundance of caution, Schnall said.

The cancellation of Saturday celebration was posted Friday on the Twitter account of the North County Transit District. The agency has scheduled a 2:30 p.m. news conference to discuss the braking issue and perhaps announce whether the system would be shut down.

Sprinter riders in Escondido and San Marcos said Friday that a shutdown would not only inconvenience their daily routines, but also cause them to spend more money to reach their destinations. Several said it would take 30 to 60 minutes longer for each leg of their commute if they had to rely on other transportation.

“I’d have to take the bus. It would take longer to get to school,” said Kiah Gravesen, 17, a junior at Vista Visions, an independent study school. Gravesen, who was at the Escondido transit center waiting for her train to the school, estimated that it would take her an hour longer each way due to waits for connecting buses.

Most of the Sprinter riders interviewed Friday said they trusted the transit district to ensure the safety of the train system. A minority did express concern about maintenance and repair of the trains.

“I feel always a little scared riding it, because you never know,” said Lisbet Penalosa, 20, a medical assistant who commutes from San Marcos to her work office in Escondido. “I feel a little more scared now.”

The unusually quick brake wear was discovered by state regulators during an inspection last week. It involves the center braking system, one of the train’s 12 brakes. Several components of the brake are wearing faster than the transit district anticipated, putting the brakes out of compliance with the system’s safety plan.

Sprinter maintenance has been outsourced since its inception, a precursor to the district’s major privatization initiative in 2009. Trains are maintained by Illinois-based contractor Veolia Transporation and Bombardier, a major private transportation company that serves as the maintenance subcontractor.

Matthew Tucker, executive director of the transit district, said a preliminary investigation revealed that the subcontractor knew about the issue with the brakes, as did the district’s rail mechanical engineer. The information somehow did not make it to higher ups at the agency, and the engineer who oversees maintenance contracts has been let go, Tucker added.

Because the Sprinter’s 12 diesel multiple unit trains are fabricated in Europe and parts are not readily available in the United States, the transit district’s officials said Friday a shutdown could last several weeks to as long as four months.

The 22-mile Sprinter system transports more than 2.4 million passengers annually between Oceanside and Escondido. The $477.6 million Sprinter began operating on March 9, 2008, two decades after voters originally passed the TransNet tax, which set aside funding for the project, and 16 years after the transit district purchased the line from the Santa Fe Railway.